Wireless communication apparatus and wireless communication system

ABSTRACT

A wireless communication system includes two wireless communication apparatuses. One of the wireless communication apparatuses wirelessly transmits a signal obtained by up-converting a clock signal. The other of the wireless communication apparatuses generates a clock signal based on a received signal and feeds back a signal obtained by up-converting the generated clock signal to the one wireless communication apparatus. The one wireless communication apparatus generates a clock signal based on the fed-back signal, detects a phase change due to a fluctuation in a transmission path characteristic based on the generated clock signal, and adjusts a phase of a reference clock signal based on the detected phase change.

BACKGROUND Field

The present disclosure relates to a wireless communication apparatus anda wireless communication system.

Description of the Related Art

A technique is known in which an apparatus equipped with a referenceclock signal source (hereinbelow, referred to as a clock sourceapparatus) wirelessly transmits a signal synchronized with a referenceclock signal, and an apparatus that receives the transmitted signal(hereinbelow, referred to as a clock reproduction apparatus) reproducesa clock signal based on the received signal. In Japanese PatentApplication Laid-Open No. 2014-116982, a technique is discussed in whichcontrol information is obtained from a state of synchronization betweena clock signal reproduced by a clock reproduction apparatus and areference clock signal. The control information is then fed back to aclock source apparatus, and the clock source apparatus adjusts a phaseof a signal the clock source apparatus transmits based on the controlinformation.

In an environment in which an antenna position for communication changesor an object moves near a wireless transmission path, a signal phase canchange due to a Doppler shift, which is caused by a change in distanceof the wireless transmission path, or an influence of multipathpropagation, for example. Hereinbelow, such a phase change is referredto as a phase change due to a fluctuation in a wireless transmissionpath characteristic.

A method discussed in Japanese Patent Application Laid-Open No.2014-116982 provides synchronization between a signal received by theclock reproduction apparatus and a clock signal reproduced from thereceived signal. The signal received by the clock reproduction apparatusis synchronized with a reference clock signal, thus in a case where aphase change due to a fluctuation in a wireless transmission pathcharacteristic does not occur, the reference clock signal of the clocksource apparatus, the signal received by the clock reproductionapparatus, and the reproduced clock signal are in a synchronized state.However, there is an issue that, in a case where the phase change due toa fluctuation in the wireless transmission path characteristic occurs,the reference clock signal of the clock source apparatus and the clocksignal reproduced by the clock reproduction apparatus may be not insynchronization with each other.

SUMMARY

Various embodiments of the present disclosure are directed to permittingsynchronization of clock signals between apparatuses that wirelesslycommunicate with each other even in an environment in which a phasechange occurs due to a fluctuation in a wireless transmission pathcharacteristic.

According to one embodiment of the present disclosure, a wirelesscommunication system includes a first wireless communication apparatus,and a second wireless communication apparatus, where the first wirelesscommunication apparatus includes a first transmission circuit unit, afirst reception circuit unit, a phase adjustment unit, and a firstantenna unit, and where the second wireless communication apparatusincludes a second reception circuit unit, a second transmission circuitunit, and a second antenna unit. The first transmission circuit unitwirelessly transmits, using the first antenna unit, a first signalgenerated based on a first clock signal. The second wirelesscommunication apparatus receives the first signal using the secondantenna unit, and the second reception circuit unit generates a secondclock signal based on the first signal. The second transmission circuitunit wirelessly transmits from the second antenna unit to the firstwireless communication apparatus, a second signal generated based on thesecond clock signal The first reception circuit unit generates a thirdclock signal based on the second signal received by the first antennaunit. The phase adjustment unit detects a change in a phase due to afluctuation in a transmission path characteristic, based on the thirdclock signal, and controls a phase of the first clock signal based onthe detected change in the phase.

Further features of the present disclosure will become apparent from thefollowing description of example embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of a wireless communication systemaccording to a first example embodiment.

FIG. 2 illustrates a configuration of a clock source apparatus accordingto the first example embodiment.

FIG. 3 illustrates a configuration of a clock reproduction apparatusaccording to the first example embodiment.

FIG. 4 illustrates a configuration of a phase adjustment unit accordingto the first example embodiment.

FIG. 5 illustrates a phase relationship of clock signals according tothe first example embodiment.

FIG. 6 illustrates a configuration of a transmission circuit unitaccording to the first example embodiment.

FIG. 7 illustrates a configuration of a reception circuit unit accordingto the first example embodiment.

FIG. 8 illustrates a configuration of a clock source apparatus accordingto a second example embodiment.

FIG. 9 is a flowchart illustrating a flow of operations according to thesecond example embodiment.

FIG. 10 is a time chart of each component block according to the secondexample embodiment

DESCRIPTION OF THE EMBODIMENTS

Example embodiments of the present disclosure will be described indetail below. The example embodiments described below do not necessarilyrestrict the present invention. All of the combinations of the featuresdescribed in the example embodiments are not always essential to themeans for solution according to each embodiment of the presentdisclosure.

A configuration of an entire wireless communication system according toa first example embodiment is described below. FIG. 1 illustrates theconfiguration of the wireless communication system according to thepresent example embodiment. A clock source apparatus 100 is one of twoapparatuses that synchronize clock signals therebetween. The clocksource apparatus 100 includes a reference clock signal source 101 thatgenerates a reference clock signal Sr, a processing unit 102 thatperforms various types of processing on the clock signal, and an antennaunit 103 that wirelessly transmits and receives signals. A clockreproduction apparatus 104 is the other of the two apparatuses thatsynchronize the clock signals therebetween. The clock reproductionapparatus 104 includes an antenna unit 105 that wirelessly transmits andreceives signals, and a processing unit 106 that processes the receivedsignal to reproduce the clock signal.

The clock source apparatus 100 generates the reference clock signal Srby the reference clock signal source 101, processes the reference clocksignal Sr by the processing unit 102, and then wirelessly transmits thesignal by the antenna unit 103. The clock reproduction apparatus 104receives the signal transmitted from the antenna unit 103 by the antennaunit 105, processes the signal by the processing unit 106 to reproduce aclock signal Srx, and feeds back the signal from the antenna unit 105 tothe antenna unit 103. Based on the phase of the signal received by theantenna unit 103, the clock source apparatus 100 processes the signal tobe transmitted again by the processing unit 102, and transmits theprocessed signal from the antenna unit 103. As described above, thewireless communication system according to the present exampleembodiment repeatedly performs feedback between the apparatuses bytransmitting signals.

Next, configurations and functions of the clock source apparatus 100 andthe clock reproduction apparatus 104 are described in more detail. FIG.2 illustrates the configurations of the processing unit 102 and theantenna unit 103 connected to the processing unit 102. The processingunit 102 includes a phase adjustment unit 201, a transmission circuitunit 202, and a reception circuit unit 203. The antenna unit 103includes a transmission antenna 103A and a reception antenna 103B. Thephase adjustment unit 201 generates a clock signal Stx, which isobtained by adjusting a phase of the reference clock signal Sr inputfrom the reference clock signal source 101 based on a clock signal Sfinput from the reception circuit unit 203. The transmission circuit unit202 up-converts the clock signal Stx generated by the phase adjustmentunit 201 and transmits the signal as a wireless signal from thetransmission antenna 103A to a wireless transmission path. The receptioncircuit unit 203 down-converts a wireless signal received by thereception antenna 103B and inputs the down-converted signal to the phaseadjustment unit 201 as the clock signal Sf. In an environment in which awireless transmission path characteristic fluctuates, the phaseadjustment unit 201 detects a phase change due to a fluctuation in thewireless transmission path characteristic based on a fed-back wirelesssignal. The phase adjustment unit 201 generates the clock signal Stx,which is obtained by adjusting a phase of the reference clock signal Srbased on a detection result of the phase change.

FIG. 3 illustrates configurations of the processing unit 106 and theantenna unit 105 connected to the processing unit 106. The processingunit 106 includes a reception circuit unit 301 and a transmissioncircuit unit 302. The antenna unit 105 includes a reception antenna 105Aand a transmission antenna 105B. The reception circuit unit 301down-converts a wireless signal received by the reception antenna 105Ato reproduce the clock signal Srx and inputs the clock signal Srx to thetransmission circuit unit 302. The transmission circuit unit 302up-converts the clock signal Srx input from the reception circuit unit301 and transmits the signal from the transmission antenna 105B to thewireless transmission path. As described above, in the wirelesscommunication system according to the present example embodiment, theclock source apparatus adjusts the phase of the clock signal, and theclock reproduction apparatus reproduces the clock signal based on thereceived signal without adjusting the phase of the clock signal, andfeeds back the received signal to the clock source apparatus.

Next, how the received signal fed back is processed by the clock sourceapparatus, and how the phase of the clock signal Stx to be transmittedis adjusted are described. FIG. 4 illustrates a circuit configuration ofthe phase adjustment unit 201 illustrated in FIG. 2 . The phaseadjustment unit 201 includes phase comparators 401 and 402, a loopfilter 403, and a voltage controlled oscillator 404. The phasecomparator 401 compares a phase of the reference clock signal Sr with aphase of an output signal (clock signal Stx) of the voltage controlledoscillator 404 and outputs a detection result (a phase differencesignal) corresponding to the phase difference. The phase comparator 402compares the phase of the reference clock signal Sr with a phase of theclock signal Sf obtained from the wireless signal fed back from theclock reproduction apparatus 104 and outputs a detection result (a phasedifference signal) corresponding to the phase difference. The loopfilter 403 includes a differential integration circuit that receives thedetection results respectively output from the phase comparators 401 and402 as input. The loop filter 403 generates a signal corresponding to adifference between the two input detection results and outputs a directcurrent component from which a harmonic component is removed. Thevoltage controlled oscillator 404 generates a signal with a phasecorresponding to the output of the loop filter 403 as the clock signalStx. The phase adjustment unit 201 is a feedback control circuit thatmakes the phases of the clock signals compared by the two phasecomparators 401 and 402 equal.

FIG. 5 illustrates a phase relationship of the clock signals compared inthe phase adjustment unit 201. FIG. 5 illustrates the phase relationshipof the clock signals in a case where the reference clock signal Sr andthe clock signal Srx reproduced by the clock reproduction apparatus arein a synchronized state. Here, it is assumed that the wirelesstransmission path characteristic is symmetrical, and a phase changeamount due to the fluctuation in the wireless transmission pathcharacteristic is defined as Δθ. Since the transmitted wireless signalis fed back and travels back and forth in the wireless transmissionpath, a phase difference between the clock signal Stx and the clocksignal Sf is 2Δθ. Further, there is a phase difference Δθ1 between thereference clock signal Sr and the clock signal Stx, and there is a phasedifference Δθ2 between the clock signal Sf and the reference clocksignal Sr. The phase adjustment unit 201 detects the phase differenceΔθ1 by the phase comparator 401, detects the phase difference Δθ2 by thephase comparator 402, and adjusts the phase of the clock signal Stx sothat the phase differences Δθ1 and Δθ2 are equal (Δθ1=Δθ2). In a casewhere the phase differences are Δθ1=Δθ2(=Δθ), the phase of the referenceclock signal Sr is equal to the phase of the clock signal Srx, and theclock signals can be synchronized between the apparatuses.

In short, the phase adjustment unit 201 detects the phase change amountdue to the fluctuation in the wireless transmission path characteristicfrom the fed-back wireless signal and generates the clock signal Stxobtained by adding an opposite phase change to the phase change to theclock signal Sr. Accordingly, the clock signal Srx, obtained by additionof the phase change due to the fluctuation in the wireless transmissionpath characteristic to the transmitted wireless signal, is synchronizedwith the reference clock signal Sr.

FIG. 6 illustrates a configuration of the transmission circuit unit 202illustrated in FIG. 2 . While FIG. 6 illustrates only the transmissioncircuit unit 202, the transmission circuit unit 302 illustrated in FIG.3 has the same configuration.

In FIG. 6 , a phase locked loop (PLL) circuit 600 includes a phasecomparator 601, a loop filter 602, a voltage controlled oscillator 603,and a frequency divider 604. The PLL circuit 600 up-converts an inputsignal by changing a frequency division number of the frequency divider604. A band-pass filter 605 is an ideal band-pass filter that attenuatesan unnecessary signal and passes only a frequency of an output signal aof the PLL circuit 600, and transmits a signal a having a desiredfrequency to the antenna 103A.

FIG. 7 illustrates a configuration of the reception circuit unit 301illustrated in FIG. 3 . While FIG. 7 illustrates only the receptioncircuit unit 301, the reception circuit unit 203 illustrated in FIG. 2has the same configuration. The reception circuit unit 301 includes aPLL circuit 700, a frequency divider 705, and a band-pass filter 706.The PLL circuit 700 that includes a phase comparator 701, a loop filter702, a voltage controlled oscillator 703, and a frequency divider 704has a function of reducing a phase noise of an input signal. Theband-pass filter 706 has the same function as that of the band-passfilter 605 and passes only the signal a having the desired frequency.The reception circuit unit 301 down-converts the signal a that haspassed through the band-pass filter 706 by the frequency divider 705,outputs the clock signal Srx via the PLL circuit 700, and transmits theclock signal Srx to the transmission circuit unit 302.

It is necessary to use different frequencies for communication betweenthe antennas 103A and 105A and for communication between the antennas103B and 105B in order to prevent interference. A signal of a frequencyf₁ is used for the communication between the antennas 103A and 105A, anda signal of a frequency f₂ is used for the communication between theantennas 103B and 105B. In the communication between the antennas 103Aand 105A, the transmission circuit unit 202 uses the frequency divider604 having the frequency division number with which the output signal aof the PLL circuit 600 becomes the frequency f₁, and the band-passfilter 605 that allows only a signal of the frequency f₁ to pass. Thereception circuit unit 301 also uses the band-pass filter 706 thatallows only the signal a of the frequency f₁ to pass. Similarly, thefrequency divider 604 and the band-pass filters 605 and 706 that cancommunicate at the frequency f₂ are used in the communication betweenthe antennas 103B and 105B, and thus two wireless transmission pathsbetween the antennas 103A and 105A and the antennas 103B and 105B areseparated.

In the present example embodiment, non-modulated communication isperformed, but the present invention is not limited thereto, and amodulation method such as amplitude modulation (AM) may be used.

With the above-described configuration, the present example embodimentcan provide a system that can wirelessly synchronize clock signals oftwo apparatuses even in an environment in which a phase change occursdue to a fluctuation in a wireless transmission path characteristic.

A configuration of an entire wireless communication system according toa second example embodiment is described below. The configuration of thewireless communication system according to the present exampleembodiment is identical to that according to the first exampleembodiment except that a changeover switch (SW) for switching input of areference clock signal is added to the processing unit 102 according tothe first example embodiment. Thus, the configuration different from thefirst example embodiment is mainly described.

The PLL circuits 600 and 700 provided respectively in the transmissioncircuit units 202 and 302 and the reception circuit units 203 and 301used in the first example embodiment require a certain time length afterstartup to output a signal with a stable phase. The required time lengthis referred to as a pull-in time. Similarly, in the phase adjustmentunit 201, there is also generated a pull-in time until a clock signalbecomes the phase relationship illustrated in FIG. 5 and a signal with astable phase is output. In the pull-in time, the fed-back clock signalSf includes the phase change of the output of the PLL circuit inaddition to the phase change due to the fluctuation in the wirelesstransmission path characteristic. Thus, in the present exampleembodiment, a configuration is described in which the phase adjustmentunit 201 detects only the phase change due to the fluctuation in thewireless transmission path characteristic, so that the pull-in timeuntil the clock signal having the phase relationship illustrated in FIG.5 is output can be shortened.

FIG. 8 illustrates a configuration in which a SW 801 and a control unit802 are added to the clock source apparatus 100. The SW 801 is a switchfor switching input of the reference clock signal Sr between thetransmission circuit unit 202 side and the phase adjustment unit 201side. The control unit 802 controls a timing of switching the SW 801.

Next, a flow of operations from startup of the system to startup of thephase adjustment unit 201 according to the present example embodiment isdescribed with reference to FIG. 9 . First, in step S901, immediatelyafter the startup of the system, the control unit 802 controls the SW801 so that the reference clock signal Sr is input to the transmissioncircuit unit 202 side. In other words, the phase adjustment unit 201does not operate, and a wireless signal with a phase equal to that ofthe reference clock signal Sr is transmitted at this time. In step S902,the control unit 802 waits for a certain period of time in this stateuntil the phases of outputs of the PLL circuits 600 and 700, which arerespectively used in the transmission circuit units 202 and 302 and thereception circuit units 203 and 301, are stabilized. In step S903, thecontrol unit 802 determines whether the phases are stabilized, and thecontrol unit 802 waits until the fluctuation of the phase of the clocksignal Sf obtained from the fed-back wireless signal is stabilized,i.e., until output voltages of the loop filters 602 and 702 in the PLLcircuits 600 and 700 each converge within a set value. At this time, theclock signal Sf includes only the phase change due to the fluctuation inthe wireless transmission path characteristic.

If the control unit 802 determines that the phases of the signals arestabilized (YES in step S903), in step S904, the SW 801 is turned to thephase adjustment unit 201 side, and the phase adjustment unit 201operates and starts an operation as a wireless clock synchronizationsystem described in the first example embodiment.

FIG. 10 illustrates a time chart of each component block according tothe present example embodiment. A horizontal axis in FIG. 10 representsa time and represents the pull-in time until the phase of the output ofeach of the circuit units is stabilized.

In FIG. 10 , a time t0 represents a start-up time, times t1, t2, t3, andt4 each represent a pull-in time from the start-up of each of thetransmission and reception circuit units, and a time t5 represents apull-in end time of the phase adjustment unit 201 according to thepresent example embodiment. In a case where all of the circuit unitsincluding the phase adjustment unit 201 are started at the same timewithout the SW 801 being provided, the pull-in time of each of thecircuit units increases, and as a result, the pull-in time of the entiresystem increases.

According to the flow illustrated in FIG. 9 , in a case where the SW 801is turned to the transmission circuit unit 202 side of the clock sourceapparatus 100, the output phases are stabilized in the order of thetransmission circuit unit 202, the reception circuit unit 301, thetransmission circuit unit 302, and the reception circuit unit 203.Subsequently, the SW 801 is turned to the phase adjustment unit 201side, and the operation of the phase adjustment unit 201 is started formthe time t4, so that the operation of the entire system is stabilized,and the total pull-in time from the time t0 to the time t5 can beshortened compared with the first example embodiment.

While example embodiments have been described, it is to be understoodthat the invention is not limited to the disclosed example embodiments.The scope of the following claims is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures and functions.

This application claims the benefit of Japanese Patent Application No.2022-003904, filed Jan. 13, 2022, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A wireless communication system comprising: afirst wireless communication apparatus; and a second wirelesscommunication apparatus, wherein the first wireless communicationapparatus includes a first transmission circuit unit, a first receptioncircuit unit, a phase adjustment unit, and a first antenna unit, whereinthe second wireless communication apparatus includes a second receptioncircuit unit, a second transmission circuit unit, and a second antennaunit, wherein the first transmission circuit unit wirelessly transmits,using the first antenna unit, a first signal generated based on a firstclock signal, wherein the first signal is received by the second antennaunit, and the second reception circuit unit generates a second clocksignal based on the first signal, wherein the second transmissioncircuit unit wirelessly transmits, from the second antenna unit to thefirst wireless communication apparatus, a second signal generated basedon the second clock signal, wherein the first reception circuit unitgenerates a third clock signal based on the second signal received bythe first antenna unit, and wherein the phase adjustment unit detects achange in a phase due to a fluctuation in a transmission pathcharacteristic, based on the third clock signal, and controls a phase ofthe first clock signal based on the detected change in the phase.
 2. Thewireless communication system according to claim 1, wherein the firstwireless communication apparatus further includes a reference clocksignal source configured to output a reference clock signal, and whereinthe phase adjustment unit includes: a voltage controlled oscillatorconfigured to operate at a frequency based on a voltage; a first phasecomparator configured to output a first phase difference signal based ona phase difference between the reference clock signal and an outputsignal of the voltage controlled oscillator; a second phase comparatorconfigured to output a second phase difference signal based on a phasedifference between the reference clock signal and the third clocksignal; and a loop filter configured to generate a voltage of thevoltage controlled oscillator based on the first phase difference signaland the second phase difference signal.
 3. The wireless communicationsystem according to claim 2, wherein the loop filter includes adifferential integration circuit to which the first phase differencesignal and the second phase difference signal are input.
 4. The wirelesscommunication system according to claim 2, wherein the first wirelesscommunication apparatus further includes a switch configured to switchthe reference clock signal to be output to one of the first transmissioncircuit unit and the phase adjustment unit.
 5. The wirelesscommunication system according to claim 4, wherein the first wirelesscommunication apparatus further includes a control unit configured todetermine a state in which an output voltage of the loop filterconverges within a set value as a stable state and to control the switchbased on a determination result.
 6. The wireless communication systemaccording to claim 1, wherein the wireless communication system delaysstartup of the phase adjustment unit until after startup of the firsttransmission circuit unit, the first reception circuit unit, the secondtransmission circuit unit, and the second reception circuit unit.
 7. Awireless communication apparatus comprising: a transmission circuit unitconfigured to wirelessly transmit, using an antenna unit, a first signalgenerated based on a first clock signal to another wirelesscommunication apparatus; a reception circuit unit configured to generatea second clock signal based on a second signal received by the antennaunit from the another wireless communication apparatus; and a phaseadjustment unit configured to detect a change in a phase due to afluctuation in a transmission path characteristic, based on the secondclock signal, and to control a phase of the first clock signal based onthe detected change in the phase.
 8. The wireless communicationapparatus according to claim 7, wherein the second signal is generatedbased on a third clock signal generated by the other wirelesscommunication apparatus.
 9. The wireless communication apparatusaccording to claim 8, wherein the third clock signal is generated basedon the first signal.
 10. The wireless communication apparatus accordingto claim 7, wherein the wireless communication apparatus delays startupof the phase adjustment unit until after startup of the transmissioncircuit unit and the reception circuit unit.